Research efforts have focused on the use of cognitive (information processing systems) strategies for exploring the mechanisms of thinking, learning, encoding and retrieval of experience in: mania, depression, the schizophrenias, the "organic" dementias (such as Huntington's Disease, Korsakoff's Psychosis, Alzheimer's Disease) as well as in drug altered brain states. Findings have helped clarify the determinants of encoding, memory storage and retrieval that characterize the cognitive changes in these different clinical syndromes. As such, it has helped to better define some of the psychological characteristics that are expressed in these altered brain state conditions and has tied some of these to underlying biological events. Data have emerged showing specific deficits in some components of information processing, changes in processing and retrieval strategies, state dependent (specific) learning and retrieval and changes in memory consolidation, all of which are drug and clinical state specific. BIBLIOGRAPHIC REFERENCES: Weingartner, H., Miller H. and Murphy, D. L.: Mood state dependent retrieval of verbal association. J. Abnorm. Psychol. 86: 276-284, 1977. Weingartner, H. and Murphy, D. L.: Brain states and memory: State dependent storage and retrieval of information. Psychopharmacol. Bull. 13: 66-67, 1977.